Effective Microorganisms (EM®) is a "biofertiliser" soil inoculant, marketed as a crop yield enhancer. However, the literature has neither comprehensively reviewed its purported effects on harvests across multiple species nor investigated its effects on plant herbivore defence other than this group's previous research on tomatoes. Here a meta-analysis of 39 journal articles and a greenhouse experiment with nine crop species afforded a nuanced assessment of Effective Microorganisms' effects on plant growth and yield. Overall, in line with predictions, Effective Microorganisms showed significant positive effect on yield and growth (0.03 effect sizes increase) in the meta-analysis, and increased growth 16 % in the greenhouse, but with strong, and at times negative, species-specific responses. An additional potential benefit of Effective Microorganisms includes increased defence against herbivore attack, but inoculated corn (Zea mays) in a field and a greenhouse experiment exhibited decreased defences. Specifically, the field experiment demonstrated that Effective Microorganisms treatment corresponded to a 26 % reduction in predatory insect diversity on corn plants, while not improving growth or yield but did increase water uptake. A subsequent greenhouse experiment suggested likely physiological mechanisms behind the loss of predator diversity. When non-inoculated control corn plants were set upon by caterpillars of the herbivorous insect Spodoptera littoralis, the plants increased production of defensive volatile organic compounds (VOCs) by 272 %. Surprisingly, inoculation with Effective Microorganisms rendered greenhouse corn plants 51 % more palatable to S. littoralis. Further localised studies are, therefore, needed to efficiently incorporate Effective Microorganisms with either conventional or sustainable agricultural management systems.

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While models of species coexistence largely focus on how competition defines biological communities, over recent decades, a number of studies show positive plant-plant species interactions (facilitation) can also promote stable coexistence. The long-lived, co-dominant shrubs California buckwheat Eriogonum fasciculatum and California sagebrush Artemisia californica share a well-documented positive association at the habitat level in their native California coastal sage scrub ecosystem, but mechanisms underlying their interactions remain unclear at finer spatial scales. Here, a hypothesis that E. fasciculatum acidifies CSS's alkaline soils and facilitates A. californica through amelioration of alkalinity stress is tested in a greenhouse experiment and association tests in the field. Greenhouse results demonstrate facilitation at early growth stages. In late growth stages, water competition is known to determine the shrubs' interactions with each other, but here, field observations of the shrubs in late growth stages show positive associations between A. californica and E. fasciculatum that have a positive linear relationship to increasing soil pH. These results highlight the importance of understanding lifecycle-long interactions among species in evaluating facilitation's impacts on community structure.